Calmodulin antagonism and inhibition of erythrocyte plasma membrane Ca(2+)-pump by nifedipine, a calcium channel blocker.

: Nifedipine, a 1,4-dihydropyridine Ca(2+)-channel blocker inhibits calmodulin-stimulated activity of erythrocyte plasma membrane (Ca(2+) + Mg2+)-ATPase. Its inhibition of the basal activity of the enzyme increases on pre-incubation with membranes. The maximum velocity, affinity for ATP and Ca(2+)-sensitivity of pump are reduced by micromolar amounts of the antihypertensive drug. These results suggest that 1,4-dihydropyridines may interact with calcium-binding proteins and calcium-dependent enzymes at their calcium-binding sites.